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Topic: I2C freezes code when using HCMS29xx lib (Read 41 times) previous topic - next topic


May 10, 2019, 03:59 am Last Edit: May 10, 2019, 11:04 am by scott_fx
I am trying to incorporate a MCP4725 dac into my project. The one issue is that it freezes my code on the end of the transmission. Here is my test code (stripped down for debugging)

Code: [Select]

#include <hcms29xx.h>
#include<Wire.h>                   //Include Wire library for using I2C functions

#define MCP4725 0x62              //MCP4725 address as 0x61 Change yours accordingly

unsigned int adc;
byte buffer[3];

// Define pins for the LED display.
#define dataPin         2 // connects to the display's data in
#define registerSelect  3 // the display's register select pin
#define clockPin        4 // the display's clock pin
#define enable          8 // the display's chip enable pin
#define reset           9 // the display's reset pin

#define displayLength   8 // number of characters in the display

// create am instance of the LED display library:
hcms29xx myDisplay = hcms29xx(dataPin, registerSelect, clockPin,
                              enable, reset, displayLength);

// screen brightness
int brightness = 15;
const int tempPin = A3;    // select the input pin for the potentiometer

int targetTemp = 0;
int targetTempOld = 0;
int hitemp = 85;        // max temp of ac unit
int lotemp = 65;      // min temp of ac unit
int displayUpdate = 0;
int count;
int modeselect = 1;
int readtemp;

void setup() {
  // initialize the display library:
  // set the brightness of the display:

void loop() {
  if (displayUpdate == 1) { //only update the display when the value changes
    count++;  //debug to see when display is updating
    Serial.println (count);
    displayUpdate = 0;  //set value to 0 until next change in value

void temp() {
  readtemp = analogRead(tempPin);
  targetTemp = map(readtemp, 1023, 0, lotemp, hitemp);
  if (targetTempOld != targetTemp) {
    displayUpdate = 1;
  targetTempOld = targetTemp;

void dacout()
  buffer[0] = 0b01000000;            //Sets the buffer0 with control byte (010-Sets in Write mode)
  adc = (modeselect) * 2048;          //multiplies the modeselect int by 2048 in order to get 0, 2.5 & 5v dac out
  if (adc == 4096) {
    adc = 4095;
  //  float ipvolt = (5.0/4096.0)* adc;  //Finding voltage formula (A0)
  buffer[1] = adc >> 4;              //Puts the most significant bit values
  buffer[2] = adc << 4;              //Puts the Least significant bit values
  delay (10);
  Serial.println ("delay");
  Wire.beginTransmission(MCP4725);         //Joins I2C bus with MCP4725 with 0x61 address
  Serial.println ("wire begin");
  Wire.write(buffer[0]);            //Sends the control byte to I2C
  Wire.write(buffer[1]);            //Sends the MSB to I2C
  Wire.write(buffer[2]);            //Sends the LSB to I2C
  delay (10);
  Serial.println ("buffer write");
  Wire.endTransmission();           //Ends the transmission
  Serial.println ("wire end");

If I comment out the "dacout();" the code runs fine.

If "dacout():" is not commented out the script freezes at the "Wire.endTransmission():"

Here is the serial monitor output:

Code: [Select]

wire begin
buffer write

Here is the display library:


I'm using an arduino nano as well

Can someone help me figure this one out?

Thanks in advance


I figured it out.  I ran an i2c scanner and it hung as well.  I probed my pcb and found out that the power trace on my PCB was missing.  I wired a jumper wire and it fixed the issue.

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